New Study: Temperature-Driven CO2 Outgassing Explains 83 Percent Of CO2 Rise Since 1959

“[T]he fraction of [fossil] fuel-related emissions still remaining in the air (about 23 ppm out of 425 ppm at the end of 2024) cannot have any climatic effect.” – Veyres et al., 2025

A few years ago Dr. Koutsoyiannis and colleagues used equations associated with the chemistry of temperature-driven organic respiration to demonstrate that, since the late 1950s, temperature-induced increases in plant and soil emissions (31.6 Gt-C/yr) account for a 3.4 times greater ratio of the >100 ppm rise in atmospheric CO2 than the contribution from the increase in fossil fuel emissions (9.4 Gt-C/yr).

This conclusion is rooted in the observation that, since 1959, the causality direction has consistently been T→CO2, and not CO2→T (Koutsoyiannis et al., 2022), when observing annual changes in atmospheric CO2 concentrations. In other words, respiration analyses indicate the rise in CO2 has been the consequence, not the cause, of temperature.

And now, in a new study, scientists have used the time-integrated effect of past sea surface temperatures and time-series modeling to establish that temperature-driven oceanic CO2 outgassing can also explain the bulk of the rise in atmospheric CO2 since the late 1950s. In contrast, there is “no correlation (R² = 0.01) between the detrended 12-month CO2 increments and fossil-fuel emissions.”

Notably, fossil fuel emissions rates can be shown to have grown from 2.4 Gt-C/yr in 1959 to 10.3 Gt-C/yr in 2025, a net +7.9 Gt-C/yr change. In contrast, natural emissions from oceanic outgassing grew from 133.2 Gt-C/yr in 1959 to 175.2 Gt-C/yr in 2025 (a net +42 Gt-C/yr change). Significantly:

“The +42 Gt-C/yr increase in temperature-driven natural inflow explains 84% of the total inflow rise since 1959…”

Other ratios detailed in the study also identify oceanic temperature-driven natural emissions as the predominant contributor to the rise in atmospheric CO2 concentration.

“[I]n 1960, oceanic degassing was 32 times the flux from ‘fossil fuels’; since 2010, it has been 11 times greater.”

“[SST anomalies] increased from 0.12°C in 1959 to 0.97°C in 2024 and accounts for 83% (+89 ppm) of the total increase (+107 ppm) in atmospheric CO2 over that period.”

“The resulting growth of [fossil fuel emissions] is 5 x 0.12 = +0.6 Gt-C/yr, or +0.28 ppm/yr – i.e. eight times smaller than the observed increase of [natural CO2 emissions] = +5 Gt-C/yr or +2.4 ppm/yr over the past decade.”

The authors identify the remaining anthropogenic contribution to the current (2024) 425 ppm atmospheric CO2 concentration as amounting to just 23 ppm, or 49 Gt-C. This means approximately ninety-five percent of today’s CO2 levels are derived from natural processes. Thus, even if the costly (€ 800 billion per year) EU decarbonization policies intended to dramatically reduce human CO2 emissions were to be fully implemented today, it would “lower atmospheric CO2 by only about 0.5 ppm by 2035.”

Image Source: Veyres et al., 2025